Radial-gap type superconducting synchronous machine, magnetizing apparatus, and magnetizing method

ABSTRACT

A radial-gap type superconducting synchronous machine  1  is prepared which includes a rotor  20  having, on its peripheral side, a convex magnetic pole  21  which includes, at its distal end part, bulk superconductors  30 . When viewed in the direction of the rotational axis C 1  of the rotor  20 , the magnetic pole center side of the bulk superconductors  30  is disposed nearer to a stator  10  than the magnetic pole end side of the bulk superconductors  30 . A ferromagnet  28  is disposed on the rotational axis C 1  side of the bulk superconductors  30 . A magnetizing apparatus  100  is disposed outside the bulk superconductors  30  in the radial direction of the rotor  20 . Magnetization of the bulk superconductors  30  is performed by directing magnetic flux lines from the magnetizing apparatus  100  toward the bulk superconductors  30.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a division of U.S. application Ser. No. 15/300,220filed Jul. 14, 2017, which is a 371 application of PCT/JP2015/059155filed Mar. 25, 2015, which claims priority to Japanese PatentApplication No. 2014-069925 filed Mar. 28, 2014, the contents of each ofwhich applications is hereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to a radial-gap type superconductingsynchronous machine, a magnetizing apparatus and a magnetizing method,and more particularly to a technique for effectively increasing capturedmagnetic flux in an object to be magnetized while ensuring the practicalutility.

BACKGROUND ART

Superconducting synchronous machines, which use a superconductingmaterial for a field system or an armature, have attracted attentione.g. for the reason that a high power output can be obtained with highefficiency, and studies and proposals have been made thereon. As withcommon synchronous machines not using a superconducting material,superconducting synchronous machine can be classified broadly into aradial-gap type and an axial-gap type. Patent document 1 (JapanesePatent No. 5162654), for example, discloses a superconductingsynchronous machine of the radial-gap type (hereinafter referred to as aradial-gap type superconducting synchronous machine), and patentdocument 2 (Japanese Patent Laid-Open Publication No. 2004-235625) bythe present inventors, for example, discloses a superconductingsynchronous machine of the axial-gap type (hereinafter referred to as anaxial-gap type superconducting synchronous machine).

The radial-gap type superconducting synchronous machine of patentdocument 1 is a rotating field system-type synchronous machine in whicha field system portion of a rotor is comprised of a permanent magnet,and an armature coil, provided in an armature as a stator, is comprisedof a superconducting coil made of a superconducting material.

In the radial-gap type superconducting synchronous machine, a higherelectric current can flow in the superconducting coil as compared to acopper coil, or the like, used in a common synchronous machine.Therefore, a large magnetic field can be generated by allowing thesuperconducting coil to function as an electromagnet. This makes itpossible to produce a high power output with high efficiency.

On the other hand, the axial-gap type superconducting synchronousmachine of patent document 2 has rotors and stators arranged alternatelyin the rotational axis direction of the rotors (a stator, a rotor and astator are arranged in this order in an illustrated embodiment). Thefield system portion of the rotor is composed of a bulk superconductor.

A bulk superconductor, which is a mass of superconductor crystals, cancapture magnetic flux lines at pinning points therein when a magneticfield (magnetic flux) is introduced into the bulk superconductor at atemperature which is not more than a critical temperature at which thematrix superconductor shows a superconducting transition. This enablesthe bulk superconductor to act as a magnet having a higher magnetic fluxdensity than a permanent magnet. Thus, according to the synchronousmachine, a field system portion having a high magnetic flux density canbe obtained by allowing the bulk superconductor to capture magnetic fluxlines, whereby a high power output can be obtained with high efficiency.Further, the bulk superconductor can hold a stronger magnetic field thana superconducting coil provided that the superconducting coil has thesame size as the bulk superconductor. The synchronous machine thereforehas an advantage in terms of downsizing over a synchronous machine whichuses a superconducting coil. Furthermore, the synchronous machine doesnot require connecting wiring for supplying electric current to thefield system portion. The synchronous machine therefore has advantagesalso in terms of simplification of the device structure and enhancementin the efficiency of the device system, such as reduction in the amountof incoming heat.

The axial-gap type superconducting synchronous machine of patentdocument 2 also has an advantage in that an armature coil, provided inan armature as a stator, is configured to function also as a magnetizingcoil (magnetizing apparatus) for the bulk superconductor. Thus, themagnetizing apparatus is integrated with the synchronous machine. Thismakes it possible to magnetize the bulk superconductor conveniently in atimely manner.

The axial-gap type superconducting synchronous machine of patentdocument 2, in performing its magnetization with the armature coil, usespulse magnetization in order to prevent the magnetizing apparatus frombecoming large-sized upon the integration of the magnetizing apparatuswith the synchronous machine and thereby losing the practical utility. Asuperconductor may be magnetized by pulse magnetization or staticmagnetic field magnetization. In the case of pulse magnetization, astrong magnetic field is instantaneously applied to a bulksuperconductor, which is held at a temperature lower than itssuperconducting critical temperature, to introduce magnetic flux intothe bulk superconductor. The bulk superconductor is allowed to capturethe magnetic flux by the pinning effect, so that the bulk superconductorwill function as a magnet having a high magnetic flux density. In thecase of static magnetic field magnetization, a static magnetic field(stationary magnetic field) is applied to a bulk superconductor, whichis held at a temperature higher than its superconducting criticaltemperature, to introduce magnetic flux into the bulk superconductor.The temperature of the bulk superconductor is then lowered to atemperature lower than the superconducting critical temperature, and thebulk superconductor is held at that temperature to allow the bulksuperconductor to capture the magnetic flux by the pinning effect,thereby allowing the bulk superconductor to function as a magnet havinga high magnetic flux density. In general, an object to be magnetized,such as a bulk superconductor, can capture more magnetic flux lines bystatic magnetic field magnetization than by pulse magnetization.However, in order to generate a necessary high static magnetic field instatic magnetic field magnetization, it is necessary to produce a coilcommensurate with the size of an object to be magnetized, and to cause ahigh electric current to flow in the coil. Further, magnetization of theobject is performed by applying the static magnetic field to the objectfor a long time. The use of static magnetic field magnetization thusrequires a large-scale magnetizing apparatus using a superconductingcoil. For these reasons, the axial-gap type superconducting synchronousmachine of patent document 2 uses pulse magnetization to magnetize thebulk superconductor with the armature coil. The practical utility can beensured by the downsizing and integration of the magnetizing coil.

PRIOR ART DOCUMENTS Patent Documents

Patent document 1: Japanese Patent No. 5162654

Patent document 2: Japanese Patent Laid-Open Publication No. 2004-235625

SUMMARY OF THE INVENTION Problems to be Solved by the Invention

A demand exists these days for the practical use of a high-power(ultrahigh-power) superconducting synchronous machine which can besuitably applied in a ship propulsion system, a generator that usesrenewable energy, etc. In this regard, to increase the magnetic fluxdensity of a field system portion is a conceivable approach. However, inthe case of the axial-gap type superconducting synchronous machine ofpatent document 2 which uses the bulk superconductor that can capture ahigh magnetic flux density, but on the other hand uses pulsemagnetization, there is a limit to a magnetic flux density that can becaptured by the bulk superconductor. If an attempt is made to employstatic magnetic field magnetization in the synchronous machine, alarge-scale magnetizing apparatus using a superconducting coil will beneeded as described above. Since the size of the entire synchronousmachine should thus be increased, this attempt is not always desirablein the light of practical utility. In particular, in static magneticfield magnetization, a coil is generally disposed such that it surroundsthe periphery of an object to be magnetized. If in the synchronousmachine of patent document 2 a coil is disposed such that it surroundsthe bulk superconductor provided in the rotor, the rotor will increasein size excessively and wiring will become complicated, whereby thepractical utility will be lost.

From such viewpoints, the present inventors have made intensive studieson a technique which uses static magnetic field magnetization and yetensures practical utility, and which can secure a lot of capturedmagnetic flux in a field system portion of a superconducting synchronousmachine. It has now been found that by devising the construction of afield system portion of a superconducting synchronous machine or theconstruction of a magnetizing apparatus, the amount of captured magneticflux in an object to be magnetized can be effectively increased whileensuring the practical utility. The finding led to the presentinvention.

The present invention has been made in view of the above situation. Itis therefore an object of the present invention to provide a radial-gaptype superconducting synchronous machine, a magnetizing apparatus and amagnetizing method which can effectively increase captured magnetic fluxin an object to be magnetized while ensuring the practical utility.

Means for Solving the Problems

A radial-gap type superconducting synchronous machine according to thepresent invention comprises: a stator having a circular cross-sectionalshape; a rotor rotatably supported inside the stator; and asuperconductor disposed on the peripheral side of the rotor, wherein therotor includes a rotor body secured to a rotating shaft, and a convexmagnetic pole provided on the periphery of the rotor body, wherein themagnetic pole, at its distal end part, includes the superconductor,wherein when viewed in the direction of a rotational axis of the rotor,the magnetic pole center side of the superconductor is disposed nearerto the stator than the magnetic pole end side of the superconductor, andwherein a ferromagnet is disposed on the rotational axis side of thesuperconductor.

Preferably, in the radial-gap type superconducting synchronous machine,the superconductor is disposed in plural numbers at the distal end partof the magnetic pole, and the plurality of superconductors are disposedin such a stepped arrangement that when viewed in the direction of therotational axis of the rotor, a superconductor closest to the center ofthe magnetic pole is located nearer to the stator than the othersuperconductors.

In the radial-gap type superconducting synchronous machine, thesuperconductor preferably has a rectangular shape as viewed from outsidein the radial direction of the rotor.

Preferably, in the radial-gap type superconducting synchronous machine,the superconductor is disposed in plural numbers at the distal end partof the magnetic pole, and the plurality of superconductors are disposedat the distal end part of the magnetic pole such that they are arrangedin the circumferential direction of the rotor, and that they arearranged in the direction of the rotational axis of the rotor.

A magnetizing apparatus according to the present invention comprises: ahousing made of a ferromagnetic material, including a top wall portion,a peripheral wall portion vertically extending downward from aperipheral portion of the top wall portion, and a core portion locatedinside the peripheral wall portion and vertically extending downwardfrom the inner surface of the top wall portion; a coil housed in thehousing, the coil being wound around the core portion and covered by thetop wall portion and the peripheral wall portion; and a current supplysection for supplying an electric current to the coil, wherein theperipheral wall portion opens in the opposite direction from the topwall portion, and the height of the peripheral wall portion from the topwall portion is larger than the height of the core portion from the topwall portion, and wherein a disposition space for an object to bemagnetized is formed in an area located opposite the distal end part ofthe core portion and located inside the peripheral wall portion.

In the magnetizing apparatus, the peripheral wall portion is preferablyprovided with a bottom wall portion made of a ferromagnetic material,extending from the distal end part of the peripheral wall portion towardthe core portion; the bottom wall portion, when viewed in the directionin which the core portion vertically extends downward, extends to aposition not overlapping the core portion; and the disposition space isformed in an area located opposite the distal end part of the coreportion and located inside the inner periphery of the bottom wallportion.

A magnetizing method according to the present invention is a method formagnetizing a radial-gap type superconducting synchronous machineincluding a stator having a circular cross-sectional shape, a rotorrotatably supported inside the stator, and a superconductor disposed onthe peripheral side of the rotor, said method comprising the steps of:preparing the radial-gap type superconducting synchronous machinewherein the rotor includes a rotor body secured to a rotating shaft, anda convex magnetic pole provided on the periphery of the rotor body,wherein the magnetic pole, at its distal end part, includes thesuperconductor, wherein when viewed in the direction of a rotationalaxis of the rotor, the magnetic pole center side of the superconductoris disposed nearer to the stator than the magnetic pole end side of thesuperconductor, and wherein a ferromagnet is disposed on the rotationalaxis side of the superconductor; disposing a magnetizing apparatusoutside the superconductor in the radial direction of the rotor; andperforming magnetization by directing magnetic flux lines from themagnetizing apparatus toward the superconductor.

The magnetizing apparatus preferably comprises: a housing made of aferromagnetic material, including a top wall portion, a peripheral wallportion vertically extending downward from a peripheral portion of thetop wall portion, and a core portion located inside the peripheral wallportion and vertically extending downward from the inner surface of thetop wall portion; a coil housed in the housing, the coil being woundaround the core portion and covered by the top wall portion and theperipheral wall portion; and a current supply section for supplying anelectric current to the coil, wherein the peripheral wall portion opensin the opposite direction from the top wall portion, and the height ofthe peripheral wall portion from the top wall portion is larger than theheight of the core portion from the top wall portion, and wherein adisposition space for an object to be magnetized is formed in an arealocated opposite the distal end part of the core portion and locatedinside the peripheral wall portion, and, in the step of disposing themagnetizing apparatus, the magnetizing apparatus is preferably disposedsuch that the superconductor of the radial-gap type superconductingsynchronous machine is located in the disposition space of themagnetizing apparatus.

The present invention also provides a magnetizing method for magnetizinga radial-gap type superconducting synchronous machine including a statorhaving a circular cross-sectional shape, a rotor rotatably supportedinside the stator, and a superconductor disposed on the peripheral sideof the rotor, said method comprising the steps of: preparing amagnetizing apparatus comprising: a housing made of a ferromagneticmaterial, including a top wall portion, a peripheral wall portionvertically extending downward from a peripheral portion of the top wallportion, and a core portion located inside the peripheral wall portionand vertically extending downward from the inner surface of the top wallportion; a coil housed in the housing, the coil being wound around thecore portion and covered by the top wall portion and the peripheral wallportion; and a current supply section for supplying an electric currentto the coil, wherein the peripheral wall portion opens in the oppositedirection from the top wall portion, and the height of the peripheralwall portion from the top wall portion is larger than the height of thecore portion from the top wall portion, and wherein a disposition spacefor an object to be magnetized is formed in an area located opposite thedistal end part of the core portion and located inside the peripheralwall portion; disposing the magnetizing apparatus outside thesuperconductor of the radial-gap type superconducting synchronousmachine in the radial direction of the rotor, with the superconductorbeing located in the disposition space of the magnetizing apparatus, andthe distal end part of the core portion of the magnetizing apparatusbeing oriented toward the superconductor; and performing magnetizationby directing magnetic flux lines from the magnetizing apparatus towardthe superconductor.

In the magnetizing apparatus, the peripheral wall portion is preferablyprovided with a bottom wall portion made of a ferromagnetic material,extending from the distal end part of the peripheral wall portion towardthe core portion; the bottom wall portion, when viewed in the directionin which the core portion vertically extends downward, extends to aposition not overlapping the core portion; and the disposition space isformed in an area located opposite the distal end part of the coreportion and located inside the inner periphery of the bottom wallportion, and, in the step of disposing the magnetizing apparatus, themagnetizing apparatus is preferably disposed such that thesuperconductor in the disposition space of the magnetizing apparatus islocated nearer to the core portion than the bottom wall portion.

In the step of performing magnetization, application of static magneticfield to the superconductor may be started under conditions that thetemperature of the superconductor is higher than its superconductingtransition temperature and, after the magnetic flux density of thestatic magnetic field has reached a predetermined target value, thetemperature of the superconductor may be lowered to a predeterminedtemperature lower than the superconducting transition temperature whilekeeping the magnetic flux density at the target value, and then themagnetic field applied by the magnetizing apparatus may be eliminated.

Advantageous Effects of the Invention

According to the radial-gap type superconducting synchronous machine ofthe present invention, when the superconductor disposed on theperipheral side of the rotor is magnetized by a magnetizing apparatusfrom outside in the radial direction of the rotor, a lot of magneticflux lines from the magnetizing apparatus pass through thesuperconductor and are guided to the ferromagnet disposed on therotational axis side of the superconductor. This enables concentratedmagnetic flux lines to pass through the superconductor. Accordingly, thesuperconductor can be magnetized with high efficiency even when, forexample, the coil of the magnetizing apparatus is disposed outside thesuperconductor in the radial direction of the rotor and at a distancefrom the superconductor, and the coil is not a large-sized onesurrounding the superconductor. A sufficient captured magnetic flux cantherefore be ensured in the superconductor even when magnetization isperformed by a magnetizing apparatus which is not large-sized. Thus,captured magnetic flux in the superconductor can be effectivelyincreased while ensuring the practical utility. This makes it possibleto increase the torque and the power output of the synchronous machine.

In the radial-gap type superconducting synchronous machine of thepresent invention, when viewed in the direction of the rotational axisof the rotor, the magnetic pole center side of the superconductor isdisposed nearer to the stator than the magnetic pole end side. Thus, thesuperconductor is disposed such that it follows the arc-shaped innersurface of the stator. This can reduce the gap between thesuperconductor and the stator, thereby making it possible to allow amagnetic field from the superconductor to efficiently act on the stator.

In the radial-gap type superconducting synchronous machine of thepresent invention, after the superconductor is magnetized by amagnetizing apparatus, the magnetized superconductor is attracted by themagnetic force to a magnetic portion of the magnetizing apparatus while,at the same time, the superconductor is attracted to the ferromagnetlocated on the rotational axis side of the superconductor. This canprevent the superconductor from moving toward the magnetizing apparatus,thus enabling the superconductor to be held in the initial installationposition.

In the case where the superconductor is disposed in plural numbers atthe distal end part of the magnetic pole, and the plurality ofsuperconductors are disposed in such a stepped arrangement that whenviewed in the direction of the rotational axis of the rotor, asuperconductor closest to the center of the magnetic pole is locatednearer to the stator than the other superconductors, the superconductorclosest to the center of the magnetic pole can be easily disposed closeto the stator.

In the case where the superconductor has a rectangular shape as viewedfrom outside in the radial direction of the rotor, the superconductorcan efficiently capture magnetic flux lines, and the total amount ofmagnetic flux in the superconductor can be increased. This can increasethe torque and the power output of the synchronous machine.

In the case where the superconductor is disposed in plural numbers atthe distal end part of the magnetic pole, and the plurality ofsuperconductors are disposed such that they are arranged in thecircumferential direction of the rotor, and that they are arranged inthe direction of the rotational axis of the rotor, a wide magnetic fluxcapturing area can be ensured with ease. This can increase the totalamount of magnetic flux in magnetic flux capturing area, therebyincreasing the torque and the power output of the synchronous machine.

According to the magnetizing apparatus of the present invention, thecoil is covered by the top wall portion and the peripheral wall portionof the housing made of ferromagnetic material, and the peripheral wallportion opens in the opposite direction from the top wall portion. Amagnetic circuit is therefore formed in which magnetic flux flows in thefollowing order: one end part (distal end part) of the core portion→theperipheral wall portion→the top wall portion→the other end part(proximal end part) of the core portion, or in the following order: theother end part (proximal end part) of the core portion→the top wallportion→the peripheral wall portion→the one end part (distal end part)of the core portion. Since the height of the peripheral wall portionfrom the top wall portion is larger than the height of the core portionfrom the top wall portion, magnetic flux lines in the magnetic circuit,coming from the one end part (distal end part) of the core portion andreaching the peripheral wall portion, or coming from the peripheral wallportion and reaching the one end part (distal end part) of the coreportion, are dense (concentrated) in the disposition space lying insidethe peripheral wall portion. This makes it possible to effectivelyensure a high magnetic flux density on a line extending from the one endpart of the core portion in the disposition space. It therefore becomespossible to pass a high-density magnetic flux through an object to bemagnetized on the line extending from the one end part of the coreportion in the disposition space, thus enabling high-efficiencymagnetization of the object even when the coil of the magnetizingapparatus is disposed at a distance from the object, and the coil is nota large-sized one surrounding the object. A sufficient captured magneticflux can therefore be ensured in the object even when magnetization isperformed by the magnetizing apparatus which is not large-sized. Thus,according to the magnetizing apparatus of the present invention,captured magnetic flux in the object can be effectively increased whileensuring the practical utility.

According to the magnetizing apparatus of the present invention,sufficient captured magnetic flux can be ensured in an object to bemagnetized even when the coil lies at a distance from the object. Thus,the degree of freedom of disposition that can ensure sufficient capturedmagnetic flux for the object can be enhanced. The practical utility canbe ensured also in this respect. Even when the magnetizing apparatus isdisposed in proximity to a magnetic pole, as an object to be magnetized,of e.g. a multi-pole rotor, the magnetizing apparatus can be preventedfrom interfering with the neighbor magnetic pole(s). Sufficient capturedmagnetic flux can therefore be ensured in each of the magnetic poles ofthe rotor.

In the case where the peripheral wall portion is provided with thebottom wall portion made of a ferromagnetic material, extending from thedistal end part of the peripheral wall portion toward the core portionand, when viewed in the direction in which the core portion verticallyextends downward, extending to a position not overlapping the coreportion, and the disposition space is formed in an area located oppositethe distal end part of the core portion and located inside the innerperiphery of the bottom wall portion, magnetic flux lines flow from theone end part (distal end part) of the core portion and reach the bottomwall portion, or flow from the bottom wall portion and reach the one endpart (distal end part) of the core portion. The magnetic flux lines cantherefore be made denser (more concentrated) on a line extending fromthe one end part of the core portion in the disposition space. Thismakes it possible to more effectively ensure a high magnetic fluxdensity on the line extending from the one end part of the core portionin the disposition space, thereby further increasing the efficiency ofmagnetization of an object to be magnetized.

According to the magnetizing method of the present invention whichcomprises preparing the radial-gap type superconducting synchronousmachine in which the ferromagnet is disposed on the rotational axis sideof the superconductor, and magnetizing the synchronous machine, when thesuperconductor disposed on the peripheral side of the rotor ismagnetized by a magnetizing apparatus from outside in the radialdirection of the rotor, a lot of magnetic flux lines from themagnetizing apparatus pass through the superconductor and are guided tothe ferromagnet disposed on the rotational axis side of thesuperconductor. This enables concentrated magnetic flux lines to passthrough the superconductor. Accordingly, the superconductor can bemagnetized with high efficiency even when, for example, the coil of themagnetizing apparatus is disposed outside the superconductor in theradial direction of the rotor and at a distance from the superconductor,and the coil is not a large-sized one surrounding the superconductor. Asufficient captured magnetic flux can therefore be ensured in thesuperconductor even when magnetization is performed by a magnetizingapparatus which is not large-sized. Thus, captured magnetic flux in thesuperconductor can be effectively increased while ensuring the practicalutility. This makes it possible to increase the torque and the poweroutput of the synchronous machine.

According to the magnetizing method of the present invention whichcomprises preparing the magnetizing apparatus including the coil housedin the housing made of a ferromagnetic material, and magnetizing thesynchronous machine, the coil is covered by the top wall portion and theperipheral wall portion of the housing made of ferromagnetic material,and the peripheral wall portion opens in the opposite direction from thetop wall portion. A magnetic circuit is therefore formed in whichmagnetic flux flows in the following order: one end part (distal endpart) of the core portion→the peripheral wall portion→the top wallportion→the other end part (proximal end part) of the core portion, orin the following order: the other end part (proximal end part) of thecore portion→the top wall portion→the peripheral wall portion→the oneend part (distal end part) of the core portion. Since the height of theperipheral wall portion from the top wall portion is larger than theheight of the core portion from the top wall portion, magnetic fluxlines in the magnetic circuit, coming from the one end part (distal endpart) of the core portion and reaching the peripheral wall portion, orcoming from the peripheral wall portion and reaching the one end part(distal end part) of the core portion, are dense (concentrated) in thedisposition space lying inside the peripheral wall portion. This makesit possible to effectively ensure a high magnetic flux density on a lineextending from the one end part of the core portion in the dispositionspace. It therefore becomes possible to pass a high-density magneticflux through an object to be magnetized on the line extending from theone end part of the core portion in the disposition space, thus enablinghigh-efficiency magnetization of the object even when the coil of themagnetizing apparatus is disposed at a distance from the object, and thecoil is not a large-sized one surrounding the object. A sufficientcaptured magnetic flux can therefore be ensured in the object even whenmagnetization is performed by the magnetizing apparatus which is notlarge-sized. Thus, according to the magnetizing apparatus of the presentinvention, captured magnetic flux in the object can be effectivelyincreased while ensuring the practical utility.

In the case of using the magnetizing apparatus including the coil housedin the housing made of a ferromagnetic material, sufficient capturedmagnetic flux can be ensured in an object to be magnetized even when thecoil lies at a distance from the object. Thus, the degree of freedom ofdisposition that can ensure sufficient captured magnetic flux for theobject can be enhanced. The practical utility can be ensured also inthis respect. In particular, even when the magnetizing apparatus isdisposed in proximity to a magnetic pole, as an object to be magnetized,of a multi-pole rotor, the magnetizing apparatus can be prevented frominterfering with the neighbor magnetic pole(s). Sufficient capturedmagnetic flux can therefore be ensured in each of the magnetic poles ofthe rotor.

High-efficiency magnetization of a superconductor can be performedeffectively especially when the radial-gap type superconductingsynchronous machine having the ferromagnet disposed on the rotationalaxis side of the superconductor is magnetized by means of themagnetizing apparatus including the coil housed in the housing made of aferromagnetic material.

In the case where in the magnetizing apparatus, the peripheral wallportion is provided with the bottom wall portion made of a ferromagneticmaterial, extending from the distal end part of the peripheral wallportion toward the core portion and, when viewed in the direction inwhich the core portion vertically extends downward, extending to aposition not overlapping the core portion, and the disposition space isformed in an area located opposite the distal end part of the coreportion and located inside the inner periphery of the bottom wallportion, the magnetizing apparatus is preferably disposed such that thesuperconductor in the disposition space of the magnetizing apparatus islocated nearer to the core portion than the bottom wall portion. Thisenables effective magnetization of the superconductor with ahigh-density magnetic flux.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a half cross-sectional side view of a radial-gap typesuperconducting synchronous machine according to an embodiment of thepresent invention;

FIG. 2 is a diagram of the radial-gap type superconducting synchronousmachine shown in FIG. 1, as viewed in the direction of the rotationalaxis;

FIG. 3 is a cross-sectional view taken along the line III-Ill of FIG. 2;

FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG. 3;

FIG. 5 is a perspective view of bulk superconductors provided in amagnetic pole of the radial-gap type superconducting synchronous machineshown in FIG. 1;

FIG. 6 is a perspective view of a ferromagnet provided in the radial-gaptype superconducting synchronous machine shown in FIG. 1;

FIG. 7 is a perspective view of a magnetizing apparatus according to anembodiment of the present invention, with a portion of the magnetizingapparatus being shown in cross-section;

FIGS. 8A and 8B are diagrams illustrating the magnetizing apparatusshown in FIG. 7, FIG. 8A being a vertical cross-sectional view of themagnetizing apparatus, and FIG. 8B illustrating part of magnetic fluxlines generated by the magnetizing apparatus;

FIG. 9 is a diagram showing a graph indicating effective concentrationof magnetic flux lines during magnetization with the magnetizingapparatus shown in FIG. 7;

FIG. 10 is a diagram illustrating how the radial-gap typesuperconducting synchronous machine shown in FIG. 1 is magnetized by themagnetizing apparatus shown in FIG. 7;

FIG. 11 is a diagram showing a graph illustrating an example oftemperature control of a bulk superconductor and timing of theapplication of a magnetic field in the magnetization illustrated in FIG.10;

FIG. 12 is a diagram illustrating part of magnetic flux lines upon themagnetization illustrated in FIG. 10; and

FIG. 13 is a diagram showing a table summarizing the performance of aradial-gap type superconducting synchronous machine of Example and theperformances of conventional synchronous machines of Comp. Examples 1 to3.

DESCRIPTION OF THE EMBODIMENTS

Embodiments of the present invention will now be described withreference to the drawings.

(Radial-Gap Type Superconducting Synchronous Machine)

A radial-gap type superconducting synchronous machine 1 according to anembodiment of the present invention will be described first. FIG. 1 is ahalf cross-sectional side view of the radial-gap type superconductingsynchronous machine 1.

As shown in FIG. 1, the radial-gap type superconducting synchronousmachine 1 includes a stator 10 having a circular cross-sectional shape,shown by the two-dot chain lines in FIG. 1, and a rotor 20 rotatablysupported inside the stator 10.

The radial-gap type superconducting synchronous machine 1 is a rotatingfield system-type synchronous machine; the stator 10 is provided with anot-shown armature coil, and the rotor 20 on the field system side isprovided with magnetic poles 21. The rotor 20 is secured to a rotatingshaft 2 extending on the rotational axis shown as C1 in FIG. 1, so thatthe rotor 20 can rotate, together with the rotating shaft 2, on therotational axis C1. A direction along the rotational axis C1 ishereinafter referred to as the rotational axis C1 direction, a directionperpendicular to the rotational axis C1 as the radial direction orradially, and a direction around the rotational axis C1 as thecircumferential direction.

FIG. 2 is a diagram of the radial-gap type superconducting synchronousmachine 1 as viewed in the rotational axis C1 direction. As shown inFIGS. 1 and 2, the rotor 20 includes a rotor body 22 comprising a pairof disk portions 22A, secured to the rotating shaft 2 and extending inthe radial direction, and a cylindrical drum portion 22B connecting theperipheries of the disks 22A, four convex magnetic poles 21 secured tothe periphery of the drum portion 22B of the rotor body 22, and agenerally-cylindrical vacuum cover 3 closed at both ends andhermetically covering the exteriors of the rotor body 22 and themagnetic poles 21.

In particular, four magnetic pole fixing portions 22C, each having arectangular frame-shaped cross-section and projecting outward in theradial direction, are formed on the periphery of the drum portion 22B ofthe rotor body 22 at regular intervals in the circumferential direction.Each magnetic pole 21 is fixed to the distal end part of a correspondingone of the magnetic pole fixing portions 22C. The rotor body 22 of thisembodiment is formed mainly of non-magnetic stainless steel.

The rotor body 22 and the vacuum cover 3 are each secured integrally tothe rotating shaft 2 so that the rotor body 22 and the vacuum cover 3can rotate, together with the rotating shaft 2, on the rotational axisC1.

The vacuum cover 3 is provided to form a vacuum insulating layer betweenit and the rotor body 22/the magnetic poles 21, thereby insulating therotor 20 from the outside. The vacuum cover 3 of this embodiment isformed mainly of non-magnetic stainless steel; however, it may be formedof an aluminum alloy or the like. The vacuum cover 3, in the periphery,has convex projecting portions that cover the magnetic poles 21.

FIG. 3 is a cross-sectional view taken along the line III-Ill of FIG. 2,and FIG. 4 is a cross-sectional view taken along the line IV-IV of FIG.3. As shown in FIGS. 3 and 4, the magnetic poles 21 of this embodimenteach include a cooling base member 23 having a rectangular plate-likeshape and secured to the magnetic pole fixing portion 22C of the rotorbody 22, a bulk aggregate 24 consisting of a plurality of bulksuperconductors 30, disposed radially outside the cooling base member 23and located on the distal end part side of the magnetic pole 21, and abulk fixing member 25 disposed radially outside the bulk aggregate 24and which sandwiches and fixes the bulk aggregate 24 between it and thecooling base member 23.

The cooling base members 23 of this embodiment are formed of OFHC(oxygen-free high conductivity) copper. As shown in FIG. 4, aninstallation surface 23A for installation of the bulk superconductors 30of the bulk aggregate 24 is formed in the radially outer surface of eachcooling base member 23. The installation surface 23A, when viewed in therotational axis C1 direction, has a central portion 23C locatedcentrally (in the center of the magnetic pole 21), and side portions 23Slocated on both sides of the central portion 23C. The central portion23C projects radially outward (toward the stator 10) from the sideportions 23S. Further, as shown in FIG. 3, the central portion 23C andthe side portions 23S extend parallel to the rotational axis C1direction.

On the other hand, as shown in FIG. 4, connecting portions 23Bprojecting radially inward are formed on the radially inner surface ofeach cooling base member 23. A heat-transfer member 4 made of, forexample, a copper material is connected to each connecting portion 23B.As shown in FIGS. 1 and 2, the heat-transfer members 4 extend radiallyinward from the connecting portions 23B, and are connected to a heatexchanger 5 installed in a portion, covered by the rotor 20, of therotating shaft 2.

A refrigerant such as neon, which has passed through the interior of therotating shaft 2, is supplied into the heat exchanger 5. The heat of thebulk aggregate 24 is transferred via the cooling base member 23 and theheat-transfer members 4 to the heat exchanger 5, and absorbed by theheat exchanger 5. The bulk superconductors 30 of the bulk aggregate 24,installed on the cooling base member 23, can thus be maintained at a lowtemperature (not more than their superconducting transitiontemperature).

FIG. 5 is a perspective view of the bulk superconductors 30 constitutingthe bulk aggregate 24. As shown in FIGS. 3 through 5, in this embodimentthe bulk superconductors 30 of the bulk aggregate 24 each have arectangular shape as viewed from radially outside, and also have arectangular shape in a radial cross-section. GdBCO (GdBa₂Cu₃O_(7-z)),which is a so-called high-temperature bulk superconducting material, isused as the bulk superconductors 30.

In this embodiment 15 bulk superconductors 30 are disposed in a 3×5arrangement on the installation surface 23A of each cooling base member23. In particular, as shown in FIGS. 3 through 5, when viewed in therotational axis C1 direction, one bulk superconductor 30 is disposed oneach of the central portion 23C and the side portions 23S of theinstallation surface 23A of each cooling base member 23 such that thethree bulk superconductors 30 are arranged in the circumferentialdirection of the rotational axis C1. Further, in a side view, the bulksuperconductors 30 are disposed such that 5 bulk superconductors 30 arearranged in the rotational axis C1 direction on each of the centralportion 23C and the two side portions 23S. Any two adjacent bulksuperconductors 30 are disposed in contact with each other, and thus thebulk superconductors 30 are densely aggregated.

In this embodiment the bulk aggregate 24, consisting of the bulksuperconductors 30 arranged in such a manner, has a rectangular contourelongated in the rotational axis C1 direction.

Further, as shown in FIG. 4, in this embodiment the central portion 23Cof the installation surface 23A projects radially outward (toward thestator 10) from the side portions 23S. Therefore, when viewed in therotational axis C1 direction, the bulk superconductors 30 are disposedin the stepped arrangement. Thus, when viewed in the rotational axis C1direction, the bulk superconductor 30 closest to the center of eachmagnetic pole 21 is located nearer to the stator 10 than the other bulksuperconductors 30.

On the other hand, as shown in FIG. 3, the bulk fixing member 25 issecured to the magnetic pole fixing portion 22C, and sandwiches the bulkaggregate 24 between it and the cooling base member 23 to hold the bulksuperconductors 30 of the bulk aggregate 24. The bulk fixing member 25of this embodiment is formed of a non-magnetic material.

In this embodiment a ferromagnet 28 is disposed on the rotational axisC1 side of the thus-constructed magnetic pole 21 (the bulk aggregate24). As shown in FIGS. 3 and 4, the ferromagnet 28 is disposed in closeproximity to the cooling base member 23 of the magnetic pole 21.

The ferromagnet 28 of this embodiment is formed of a ferromagnetic metalmaterial composed mainly of iron. FIG. 6 is a perspective view of theferromagnet 28. As shown in FIG. 6, the ferromagnet 28 has a rectangularplate-like shape and has through-holes 28A for passage of theabove-described heat-transfer members 4 therethrough.

As shown in FIGS. 3 and 4, the ferromagnet 28 is disposed in closeproximity to the cooling base member 23, with the heat-transfer members4 being inserted into the through-holes 28A, and is fixed to themagnetic pole fixing portion 22C. The ferromagnet 28 has a larger sizethan the bulk aggregate 24 when viewed in the radial direction, and isdisposed such that it covers the entire bulk aggregate 24 from inside.

The above-described radial-gap type superconducting synchronous machine1 is subjected to magnetization of the bulk superconductors 30 of thebulk aggregate 24 with the below-described magnetizing apparatus 100.The ferromagnet 28 can guide magnetic flux lines from the magnetizingapparatus 100 so that they pass through the bulk aggregate 24 during themagnetization and, in addition, can stably keep the bulk aggregate 24 inthe initial installation position after the magnetization of the bulkaggregate 24. The details will be described below.

(Magnetizing Apparatus)

Next, a magnetizing apparatus 100 according to an embodiment of thepresent invention will now be described. The magnetizing apparatus 100can be used to magnetize the bulk superconductors 30 of each bulkaggregate 24 of the above-described radial-gap type superconductingsynchronous machine 1. FIG. 7 is a perspective view of the magnetizingapparatus 100, FIG. 8A is a vertical cross-sectional view of themagnetizing apparatus 100, and FIG. 8B is a diagram illustrating part ofmagnetic flux lines generated by the magnetizing apparatus 100.

As shown in FIGS. 7 and 8A, the magnetizing apparatus 100 of thisembodiment includes a housing 101 made of a ferromagnetic material,including a top wall portion 101T, a peripheral wall portion 101Svertically extending downward from a peripheral portion of the top wallportion 101T, and a core portion 101C located inside the peripheral wallportion 101S and vertically extending downward from the inner surface ofthe top wall portion 101T. In particular, the housing 101 is formed of aferromagnetic metal material composed mainly of iron. In across-sectional view, the core portion 101C is located in anintermediate area between the opposing peripheral wall portions 101S.The peripheral wall portion 101S opens in the opposite direction fromthe top wall portion 101T.

In the housing 101 is housed a superconducting coil (hereinafterreferred to simply as coil) 102 wound around the core portion 101C andcovered by the top wall portion 101T and the peripheral wall portion101S. The coil 102 is formed of a superconducting material (Bi2233(Bi₂Sr₂Ca₂Cu₃O_(10+δ)) in this embodiment), and is connected to acurrent supply section 104 by a connecting wire 103 drawn out of thehousing 101. A magnetic field is generated by the coil 102 by supplyingan electric current from the current supply section 104 to the coil 102.

The housing 101 has a generally-rectangular contour, and the coreportion 101C has an elongated shape extending in the longitudinaldirection of the housing 101. The length of the core portion 101C in thelongitudinal direction is equal to the length of the bulk aggregate 24of the radial-gap type superconducting synchronous machine 1 in therotational axis C1 direction (see FIG. 3).

The coil 102, which is wound around the core portion 101C, also has agenerally-rectangular contour. The coil 102 is composed ofgenerally-rectangular multi-layer wire windings.

The housing 101 will now be described in detail. As shown in FIG. 8A,the height of the peripheral wall portion 101S from the top wall portion101T is larger than the height of the core portion 101C from the topwall portion 101T. In this embodiment, a bottom wall portion 101E,extending from the distal end part of the peripheral wall portion 101Stoward the core portion 101C, is formed integrally with the peripheralwall portion 101S. In this embodiment the bottom wall portion 101E,formed integrally with the peripheral wall portion 101S, is also made ofa ferromagnetic material.

In this embodiment, when viewed in the direction in which the coreportion 101C vertically extends (projects) downward, the bottom wallportion 101E extends to a position not overlapping the core portion101C. A disposition space D for an object to be magnetized is formed inan area located inside the inner periphery of the bottom wall portion101E and located opposite the distal end part of the core portion 101Cin the direction in which the core portion 101C vertically extends(projects) downward. Particularly in this embodiment, the object to bemagnetized is the bulk aggregate 24 of each magnetic pole 21 of theradial-gap type superconducting synchronous machine 1. Therefore, thebottom wall portion 101E has such an open structure as to be capable ofinserting the magnetic pole 21 through the space inside the innerperiphery of the bottom wall portion 101E and positioning the bulkaggregate 24 in the disposition space D.

In the above-described magnetizing apparatus 100, the coil 102 iscovered by the top wall portion 101T and the peripheral wall portion101S of the housing 101 made of ferromagnetic material, and theperipheral wall portion 101S opens in the opposite direction from thetop wall portion 101T. A magnetic circuit is therefore formed in whichmagnetic flux flows e.g. in the following order: one end part (distalend part) of the core portion 101C→the bottom wall portion 101E→theperipheral wall portion 101S→the top wall portion 101T→the other endpart (proximal end part) of the core portion 101C. Since the height ofthe peripheral wall portion 101S from the top wall portion 101T islarger than the height of the core portion 101C from the top wallportion 101T, magnetic flux lines W in the magnetic circuit, coming fromthe one end part (distal end part) of the core portion 101C and reachingthe peripheral wall portion 101S (bottom wall portion 101E), are dense(concentrated) in the disposition space D lying inside the peripheralwall portion 101S and the bottom wall portion 101E, as shown in FIG. 8B.This makes it possible to effectively ensure a high magnetic fluxdensity on a line extending from the one end part of the core portion101C in the disposition space D. It therefore becomes possible to pass ahigh-density magnetic flux through an object to be magnetized on theline extending from the one end part of the core portion 101C in thedisposition space D, thus enabling high-efficiency magnetization of theobject.

FIG. 9 shows a graph indicating effective concentration of magnetic fluxlines during magnetization with the magnetizing apparatus 100, i.e.indicating that the total magnetic flux, generated by the magnetizingapparatus 100 for an object to be magnetized, is effectively ensured.The graph shows data on the total magnetic flux of a magnetic fieldgenerated by the magnetizing apparatus 100 in comparison with data onthe total magnetic flux of a magnetic field generated by a magnetizingapparatus (comparative magnetizing apparatus) in which a portion,corresponding to the housing 101 of the magnetizing apparatus 100, isformed of an aluminum alloy which is not a ferromagnetic material. Thetotal magnetic flux refers to the total amount of magnetic flux presentin the entire disposition space D.

As can be seen in FIG. 9, the total magnetic flux of the magnetic fieldgenerated by the magnetizing apparatus 100 is considerably higher, inparticular by about 27%, than the total magnetic flux of the magneticfield generated by the comparative magnetizing apparatus.

(Magnetizing Method)

Next, a method for magnetizing the radial-gap type superconductingsynchronous machine 1 by using the magnetizing apparatus 100 will now bedescribed. FIG. 10 is a diagram illustrating how the magnetization isperformed.

When performing the magnetization with the magnetizing apparatus 100,the rotor 20 of the radial-gap type superconducting synchronous machine1 is first taken out of the stator 10. Thereafter, as shown in FIG. 10,one magnetic pole 21 of the rotor 20 is inserted into the dispositionspace D of the magnetizing apparatus 100, and the magnetizing apparatus100 comes to lie radially outside the magnetic pole 21 such that thebulk aggregate 24 of the magnetic pole 21 in the disposition space D islocated opposite to and in close proximity to the core portion 101C. Inparticular, in this embodiment the magnetizing apparatus 100 is to bedisposed such that the bulk aggregate 24 in the disposition space D islocated nearer to the core portion 101C than the inner surface of thebottom wall portion 101E of the housing 101, and that the ferromagnet 28of the radial-gap type superconducting synchronous machine 1 is locatednearer to the core portion 101C than the outer surface of the bottomwall portion 101E. In the illustrated embodiment, the magnetic pole 21of the rotor 20 is inserted into the disposition space D by lowering themagnetizing apparatus 100. The projecting portion of the vacuum cover 3,covering the magnetic pole 21, is also disposed in the disposition spaceD.

Subsequently, an electric current is supplied from the current supplysection 104 (see FIG. 7) to the coil 102 to generate a magnetic field.In this embodiment magnetization is effected by directing the magneticflux lines of the magnetizing apparatus 100 from the distal end part ofthe core portion 101C toward the bulk aggregate 24 of the radial-gaptype superconducting synchronous machine 1. In this embodiment theelectric current is continuously supplied to the coil 102 so thatmagnetization is effected by static magnetic field magnetization.

FIG. 11 is a diagram showing a graph illustrating an example oftemperature control of the bulk superconductors and timing of theapplication of a magnetic field in the magnetization according to thisembodiment. In the graph of FIG. 11, the abscissa axis represents time,and the ordinate axis represents the temperature (K) of the bulksuperconductors 30 and the magnetic flux density (T) of the magneticfield applied. The line L1 indicates the temperature of the bulksuperconductors 30, and the line L2 indicates the magnetic flux densityof the magnetic field generated by supplying an electric current to thecoil 102. Tc represents the superconducting transition temperature.

As shown in FIG. 11, in this embodiment the application of staticmagnetic field (stationary magnetic field) to the bulk superconductors30 is started under conditions that the temperature of the bulksuperconductors 30 is controlled at a temperature higher than thesuperconducting transition temperature Tc. After the magnetic fluxdensity of the static magnetic field has reached a predetermined targetvalue, the temperature of the bulk superconductors 30 is lowered to apredetermined temperature (50 K in the illustrated example) lower thanthe superconducting transition temperature Tc while keeping the magneticflux density at the target value. The bulk superconductors 30 are in asuperconducting state from the superconducting transition temperature,which allows passage of magnetic flux lines through the bulksuperconductors 30, when their temperature is lower than thesuperconducting transition temperature Tc. As shown by the graph of FIG.11, the magnetic field is applied for a predetermined period of time(about 60 minutes in the illustrated example) until the temperature ofthe bulk superconductors 30 reaches the predetermined temperature lowerthan the superconducting transition temperature Tc. By thus continuingto apply the magnetic field to the bulk superconductors 30 until theyare cooled to the sufficiently low temperature, a lot of magnetic fluxlines are captured by the bulk superconductors 30.

When the magnetic field is generated by the magnetizing apparatus 100 inthe above-described manner, a magnetic circuit is formed in which, asshown in FIG. 12, magnetic flux flows in the following order: one endpart (distal end part) of the core portion 101C→the bottom wall portion101E→the peripheral wall portion 101S→the top wall portion 101T→theother end part (proximal end part) of the core portion 101C. Since theheight of the peripheral wall portion 101S from the top wall portion101T is larger than the height of the core portion 101C from the topwall portion 101T, magnetic flux lines W in the magnetic circuit, comingfrom the one end part (distal end part) of the core portion 101C andreaching the peripheral wall portion 101S (bottom wall portion 101E),are concentrated in the disposition space D lying inside the peripheralwall portion 101S and the bottom wall portion 101E, as shown in FIG. 12.This makes it possible to effectively ensure a high magnetic fluxdensity on a line extending from the one end part of the core portion101C in the disposition space D. Further, in this embodiment, because ofthe provision of the ferromagnet 28 in the radial-gap typesuperconducting synchronous machine 1, magnetic flux lines from themagnetizing apparatus 100 are guided so that they pass through the bulkaggregate 24 and reach the ferromagnet 28. In particular, in thisembodiment, the ferromagnet 28 is located nearer to the core portion101C than the outer surface of the bottom wall portion 101E. Agenerally-rectangular magnetic circuit, running through the housing ofthe magnetizing apparatus 100 and the ferromagnet 28, is thereforeformed. Since the bulk aggregate 24 is located in the straight lineportion of the magnetic circuit, magnetic flux lines effectively passthrough the bulk aggregate 24. Magnetization of the bulk aggregate 24can therefore be performed efficiently.

After applying the magnetic field for a predetermined period of time asdescribed above, the supply of electric current to the coil 102 isstopped, i.e. the current applied to the coil 102 is made 0, whereby themagnetic field is eliminated as shown in FIG. 11. Thereafter, the rotor20 is rotated, and the magnetic pole 21 of the rotor 20, to be nextmagnetized, is disposed in the disposition space D of the magnetizingapparatus 100 and subjected to magnetization.

According to the above-described embodiment, the coil 102 is covered bythe top wall portion 101T and the peripheral wall portion 101S of thehousing 101 made of ferromagnetic material, and the peripheral wallportion 101S opens in the opposite direction from the top wall portion101T. A magnetic circuit is therefore formed in which magnetic fluxflows in the following order: one end part (distal end part) of the coreportion 101C→the bottom wall portion 101E→the peripheral wall portion101S→the top wall portion 101T→the other end part (proximal end part) ofthe core portion 101C. Since the height of the peripheral wall portion101S from the top wall portion 101T is larger than the height of thecore portion 101C from the top wall portion 101T, magnetic flux lines Win the magnetic circuit, coming from the one end part (distal end part)of the core portion 101C and reaching the peripheral wall portion 101S(bottom wall portion 101E), are dense (concentrated) in the dispositionspace D lying inside the peripheral wall portion 101S and the bottomwall portion 101E. This makes it possible to effectively ensure a highmagnetic flux density on a line extending from the one end part of thecore portion 101C in the disposition space D. It therefore becomespossible to pass a high-density magnetic flux through an object to bemagnetized on the line extending from the one end part of the coreportion 101C in the disposition space D.

Further, in this embodiment, the peripheral wall portion 101S isprovided with the bottom wall portion 101E made of a ferromagneticmaterial and extending from the distal end part of the peripheral wallportion 101S toward the core portion 101C. When viewed in the directionin which the core portion 101C vertically extends downward, the bottomwall portion 101E extends to a position not overlapping the core portion101C, and the disposition space D is formed in an area located oppositethe distal end part of the core portion 101C and inside the innerperiphery of the bottom wall portion 101E. Since the magnetic flux linesW flow from the one end part (distal end part) of the core portion 101Cand reach the bottom wall portion 101E, the magnetic flux lines can bemade more dense (concentrated) on a line extending from the one end partof the core portion 101C in the disposition space D. This furtherincreases the efficiency of magnetization of an object to be magnetized.

Further, because of the provision of the ferromagnet 28 in theradial-gap type superconducting synchronous machine 1, a lot of magneticflux lines W from the magnetizing apparatus 100 are guided so that theypass through the bulk aggregate 24 and reach the ferromagnet 28. Thus,the dense or concentrated magnetic flux lines can be passed through thebulk aggregate 24 composed of the bulk superconductors 30.

As will be appreciated from the foregoing, the bulk aggregate 24composed of the bulk superconductors 30 can be magnetized with highefficiency even though the coil 102 of the magnetizing apparatus 100 isdisposed at a distance from the bulk aggregate 24, and the coil 102 isnot a large-sized one surrounding the bulk aggregate 24. A sufficientcaptured magnetic flux can therefore be ensured in the bulk aggregate 24even though magnetization is performed by the magnetizing apparatus 100which is not large-sized. Thus, according to this embodiment, capturedmagnetic flux in the bulk aggregate 24 composed of the bulksuperconductors 30 can be effectively increased while ensuring thepractical utility. This makes it possible to increase the torque and thepower output of the synchronous machine.

In the magnetizing apparatus 100 of this embodiment, sufficient capturedmagnetic flux can thus be ensured in the bulk aggregate 24 even thoughthe coil 102 lies at a distance from the bulk aggregate 24. Therefore,the degree of freedom of disposition that can ensure sufficient capturedmagnetic flux for the bulk aggregate 24 can be enhanced. The practicalutility can be ensured also in this respect. In particular, even thoughthe magnetizing apparatus 100 is disposed in proximity to the bulkaggregate 24 of a magnetic pole 21, as an object to be magnetized, ofthe rotor 20 which is a multi-pole rotor in this embodiment, themagnetizing apparatus 100 can be prevented from interfering with theneighbor magnetic pole(s). Sufficient captured magnetic flux cantherefore be ensured in each of the plurality of magnetic poles.

Further, in the radial-gap type superconducting synchronous machine 1 ofthis embodiment, when viewed in the direction of the rotational axis C1of the rotor 20, the magnetic pole center side of the bulk aggregate 24is disposed nearer to the stator 10 than the magnetic pole end side.Thus, the bulk aggregate 24 is disposed such that it follows thearc-shaped inner surface of the stator 10. This can reduce the gapbetween the bulk aggregate 24 and the stator 10, thereby making itpossible to allow a magnetic field from the bulk aggregate 24 toefficiently act on the stator 10.

Further, in the radial-gap type superconducting synchronous machine 1 ofthis embodiment, after the bulk aggregate 24 is magnetized by themagnetizing apparatus 100, the magnetized bulk aggregate 24 is attractedby the magnetic force to the housing 101 of ferromagnetic material,constituting the magnetizing apparatus 100, while, at the same time, thebulk aggregate 24 is attracted to the ferromagnet 28 located on therotational axis C1 side of the bulk aggregate 24. This can prevent thebulk aggregate 24 from moving toward the magnetizing apparatus 100, thusenabling the bulk aggregate 24 to be held in the initial installationposition.

EXAMPLES

An example of the radial-gap type superconducting synchronous machine 1will now be described. FIG. 13 is a diagram showing a table summarizingthe performance of a radial-gap type superconducting synchronous machineof Example and the performances of conventional superconductingsynchronous machines of Comp. Examples 1 to 3.

The table of FIG. 13 shows data on the “model” of each of thesynchronous machines of Example and Comp. Examples 1 to 3, “rotationalspeed”, “torque” and “power output” as exemplary performance parameters,“superconducting material” used for a field system or an armature,“refrigerant or cooling method” for maintaining the superconductingmaterial at a low temperature, and “captured magnetic flux density” in amagnetic pole.

The radial-gap type superconducting synchronous machine 1 of Example wasmagnetized by the magnetizing apparatus 100 in the manner describedabove with reference to the above embodiment, whereby magnetic fluxlines were captured by the bulk aggregate 24 of each magnetic pole 21.In Example, GdBCO was used for the bulk superconductors 30, and neon wasused for the refrigerant. Further, for the radial-gap typesuperconducting synchronous machine 1 of Example, it was estimated thata very high captured magnetic flux density of, for example, 5.0 Tesla(T) is obtained, and a very high torque of 1508 Nm is obtained at arotational speed of 190 rpm. The power output at that rotational speedwas estimated to be 30 kW.

The synchronous machine of Comp. Example 1 is a reluctance-typesuperconducting synchronous machine (radial-gap type) that uses a YBCO(YBa₂Cu₃O_(7-z)) high-temperature superconducting bulk for a magneticsystem pole, and liquid nitrogen as a refrigerant. As shown in thetable, the comparative synchronous machine was found to have a torque of127 Nm at a rotational speed of 3000 rpm, and a power output of 40 kW atthat rotational speed. The comparative data demonstrates that comparedto the synchronous machine of Comp. Example 1, the synchronous machineof Example can obtain a significantly higher torque at a lowerrotational speed. This indicates that the synchronous machine of Examplecan promptly obtain a high output as compared to the synchronous machineof Comp. Example 1.

The synchronous machine of Comp. Example 2 is a radial-gap typesuperconducting synchronous machine that uses a YBCO high-temperaturesuperconducting bulk for a magnetic system pole, and uses directconduction cooling as a cooling method. As shown in the table, thecomparative synchronous machine was found to have a torque of 24 Nm at arotational speed of 600 rpm, and a power output of 1.5 kW at thatrotational speed. The comparative data demonstrates that compared to thesynchronous machine of Comp. Example 2, the synchronous machine ofExample can obtain a significantly higher torque at a lower rotationalspeed. This indicates that the synchronous machine of Example canpromptly obtain a significantly higher output as compared to thesynchronous machine of Comp. Example 1.

The synchronous machine of Comp. Example 3 is an axial-gap typesuperconducting synchronous machine that uses a GdBCO superconductingmaterial for a magnetic system, and liquid nitrogen as a refrigerant,and has a captured magnetic flux density of 0.8 to 0.9 T. As shown inthe table, the comparative synchronous machine was found to have atorque of 212 Nm at a rotational speed of 720 rpm, and a power output of16 kW at that rotational speed. The comparative data demonstrates thatthe synchronous machine of Comp. Example 3 can obtain a high torque at arelatively low rotational speed, but is inferior to the synchronousmachine of Example. The comparative data indicates that the synchronousmachine of Example can promptly obtain a significantly higher output ascompared to the synchronous machine of Comp. Example 3. In Comp. Example3, the bulk superconductor was magnetized by pulse magnetization.

While the present invention has been described with reference topreferred embodiments, it is understood that the present invention isnot limited to the embodiments described above and that various changesand modifications may be made thereto. For example, though in theabove-described embodiment the bulk aggregate 24 of the radial-gap typesuperconducting synchronous machine 1 is composed of the 15 bulksuperconductors 30, the number of the bulk superconductors 30 is notlimited to 15; for example, only one bulk superconductor may be providedin each magnetic pole 21. Further, the material of the bulksuperconductors 30 is not limited to GdBCO.

Though in the above-described embodiment the radial-gap typesuperconducting synchronous machine 1 has the four magnetic poles 21,the number of the magnetic poles is not limited to four.

Though in the above-described embodiment the stator 10 of the radial-gaptype superconducting synchronous machine 1 has a cylindrical shapehaving a circular cross-section and which is relatively long in theaxial direction, the stator 10 may have an annular shape which isrelatively short in the axial direction. When the rotor 20 has arelatively large size, the stator 10 preferably has an annular shape.

Materials other than the above-described materials can, of course, beused for the rotor 20 and the vacuum cover 3. Though the bulksuperconductors 30 of the above-described embodiment have a rectangularshape as viewed from radially outside, it is possible to use othershapes such as a circular shape.

Instead of the bulk superconductors 30 used in the above-describedembodiment, a superconducting wire rod may be used in the radial-gaptype superconducting synchronous machine 1. Though the housing 101 ofthe magnetizing apparatus 100 may not necessarily have the bottom wallportion 101E, the provision of the bottom wall portion 101E can increasethe efficiency of magnetization.

DESCRIPTION OF THE REFERENCE NUMERALS

-   1 radial-gap type superconducting synchronous machine-   2 rotating shaft-   3 vacuum cover-   4 heat-transfer member-   5 heat exchanger-   10 stator-   20 rotor-   21 magnetic pole-   22 rotor body-   22A disk portion-   22B drum portion-   22C magnetic pole fixing portion-   23 cooling base member-   23A installation surface-   23B connecting portion-   23C central portion-   23S side portion-   24 bulk aggregate-   25 bulk fixing member-   28 ferromagnet-   30 bulk superconductors-   100 magnetizing apparatus-   101 housing-   101T top wall portion-   101S peripheral wall portion-   101C core portion-   101E bottom wall portion-   102 coil-   103 connecting wire-   104 current supply section

The invention claimed is:
 1. A radial-gap type superconductingsynchronous machine comprising: a stator having a circularcross-sectional shape; a rotor rotatably supported inside the stator;and a superconductor disposed on the peripheral side of the rotor,wherein the rotor includes a rotor body secured to a rotating shaft, anda convex magnetic pole provided on the periphery of the rotor body,wherein the rotor body includes a magnetic pole fixing portionprojecting outward in the radial direction, wherein the magnetic pole,includes the superconductor at a distal end of the magnetic pole whichis radially outside the magnetic pole fixing portion, wherein thesuperconductor includes one or more bulk superconductors, wherein whenviewed in the direction of a rotational axis of the rotor, the magneticpole center side of the superconductor is disposed nearer to the statorthan the magnetic pole end side of the superconductor, and wherein aferromagnet is disposed on the rotational axis side of thesuperconductor.
 2. The radial-gap type superconducting synchronousmachine according to claim 1, wherein the superconductor is disposed inplural numbers at the distal end part of the magnetic pole, and theplurality of superconductors are disposed in such a stepped arrangementthat when viewed in the direction of the rotational axis of the rotor, asuperconductor closest to the center of the magnetic pole is locatednearer to the stator than the other superconductors.
 3. The radial-gaptype superconducting synchronous machine according to claim 1, whereinthe superconductor has a rectangular shape as viewed from outside in theradial direction of the rotor.
 4. The radial-gap type superconductingsynchronous machine according to claim 1, wherein the superconductor isdisposed in plural numbers at the distal end part of the magnetic pole,and the plurality of superconductors are disposed at the distal end partof the magnetic pole such that they are arranged in the circumferentialdirection of the rotor, and that they are arranged in the direction ofthe rotational axis of the rotor.